\input texinfo @c -*-texinfo-*- @c %**start of header @setfilename gfortran.info @set copyrights-gfortran 1999-2007 @include gcc-common.texi @settitle The GNU Fortran Compiler @c Create a separate index for command line options @defcodeindex op @c Merge the standard indexes into a single one. @syncodeindex fn cp @syncodeindex vr cp @syncodeindex ky cp @syncodeindex pg cp @syncodeindex tp cp @c TODO: The following "Part" definitions are included here temporarily @c until they are incorporated into the official Texinfo distribution. @c They borrow heavily from Texinfo's \unnchapentry definitions. @tex \gdef\part#1#2{% \pchapsepmacro \gdef\thischapter{} \begingroup \vglue\titlepagetopglue \titlefonts \rm \leftline{Part #1:@* #2} \vskip4pt \hrule height 4pt width \hsize \vskip4pt \endgroup \writetocentry{part}{#2}{#1} } \gdef\blankpart{% \writetocentry{blankpart}{}{} } % Part TOC-entry definition for summary contents. \gdef\dosmallpartentry#1#2#3#4{% \vskip .5\baselineskip plus.2\baselineskip \begingroup \let\rm=\bf \rm \tocentry{Part #2: #1}{\doshortpageno\bgroup#4\egroup} \endgroup } \gdef\dosmallblankpartentry#1#2#3#4{% \vskip .5\baselineskip plus.2\baselineskip } % Part TOC-entry definition for regular contents. This has to be % equated to an existing entry to not cause problems when the PDF % outline is created. \gdef\dopartentry#1#2#3#4{% \unnchapentry{Part #2: #1}{}{#3}{#4} } \gdef\doblankpartentry#1#2#3#4{} @end tex @c %**end of header @c Use with @@smallbook. @c %** start of document @c Cause even numbered pages to be printed on the left hand side of @c the page and odd numbered pages to be printed on the right hand @c side of the page. Using this, you can print on both sides of a @c sheet of paper and have the text on the same part of the sheet. @c The text on right hand pages is pushed towards the right hand @c margin and the text on left hand pages is pushed toward the left @c hand margin. @c (To provide the reverse effect, set bindingoffset to -0.75in.) @c @tex @c \global\bindingoffset=0.75in @c \global\normaloffset =0.75in @c @end tex @copying Copyright @copyright{} @value{copyrights-gfortran} Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being ``GNU General Public License'' and ``Funding Free Software'', the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the section entitled ``GNU Free Documentation License''. (a) The FSF's Front-Cover Text is: A GNU Manual (b) The FSF's Back-Cover Text is: You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development. @end copying @ifinfo @dircategory Software development @direntry * gfortran: (gfortran). The GNU Fortran Compiler. @end direntry This file documents the use and the internals of the GNU Fortran compiler, (@command{gfortran}). Published by the Free Software Foundation 51 Franklin Street, Fifth Floor Boston, MA 02110-1301 USA @insertcopying @end ifinfo @setchapternewpage odd @titlepage @title Using GNU Fortran @versionsubtitle @author The @t{gfortran} team @page @vskip 0pt plus 1filll Published by the Free Software Foundation@* 51 Franklin Street, Fifth Floor@* Boston, MA 02110-1301, USA@* @c Last printed ??ber, 19??.@* @c Printed copies are available for $? each.@* @c ISBN ??? @sp 1 @insertcopying @end titlepage @c TODO: The following "Part" definitions are included here temporarily @c until they are incorporated into the official Texinfo distribution. @tex \global\let\partentry=\dosmallpartentry \global\let\blankpartentry=\dosmallblankpartentry @end tex @summarycontents @tex \global\let\partentry=\dopartentry \global\let\blankpartentry=\doblankpartentry @end tex @contents @page @c --------------------------------------------------------------------- @c TexInfo table of contents. @c --------------------------------------------------------------------- @ifnottex @node Top @top Introduction @cindex Introduction This manual documents the use of @command{gfortran}, the GNU Fortran compiler. You can find in this manual how to invoke @command{gfortran}, as well as its features and incompatibilities. @ifset DEVELOPMENT @emph{Warning:} This document, and the compiler it describes, are still under development. While efforts are made to keep it up-to-date, it might not accurately reflect the status of the most recent GNU Fortran compiler. @end ifset @comment @comment When you add a new menu item, please keep the right hand @comment aligned to the same column. Do not use tabs. This provides @comment better formatting. @comment @menu * Introduction:: Part I: Invoking GNU Fortran * Invoking GNU Fortran:: Command options supported by @command{gfortran}. * Runtime:: Influencing runtime behavior with environment variables. Part II: Language Reference * Fortran 2003 status:: Fortran 2003 features supported by GNU Fortran. * Extensions:: Language extensions implemented by GNU Fortran. * Intrinsic Procedures:: Intrinsic procedures supported by GNU Fortran. * Contributing:: How you can help. * Copying:: GNU General Public License says how you can copy and share GNU Fortran. * GNU Free Documentation License:: How you can copy and share this manual. * Funding:: How to help assure continued work for free software. * Option Index:: Index of command line options * Keyword Index:: Index of concepts @end menu @end ifnottex @c --------------------------------------------------------------------- @c Introduction @c --------------------------------------------------------------------- @node Introduction @chapter Introduction @c The following duplicates the text on the TexInfo table of contents. @iftex This manual documents the use of @command{gfortran}, the GNU Fortran compiler. You can find in this manual how to invoke @command{gfortran}, as well as its features and incompatibilities. @ifset DEVELOPMENT @emph{Warning:} This document, and the compiler it describes, are still under development. While efforts are made to keep it up-to-date, it might not accurately reflect the status of the most recent GNU Fortran compiler. @end ifset @end iftex The GNU Fortran compiler front end was designed initially as a free replacement for, or alternative to, the unix @command{f95} command; @command{gfortran} is the command you'll use to invoke the compiler. @menu * About GNU Fortran:: What you should know about the GNU Fortran compiler. * GNU Fortran and GCC:: You can compile Fortran, C, or other programs. * GNU Fortran and G77:: Why we chose to start from scratch. * Project Status:: Status of GNU Fortran, roadmap, proposed extensions. * Standards:: Standards supported by GNU Fortran. @end menu @c --------------------------------------------------------------------- @c About GNU Fortran @c --------------------------------------------------------------------- @node About GNU Fortran @section About GNU Fortran The GNU Fortran compiler is still in an early state of development. It can generate code for most constructs and expressions, but much work remains to be done. When the GNU Fortran compiler is finished, it will do everything you expect from any decent compiler: @itemize @bullet @item Read a user's program, stored in a file and containing instructions written in Fortran 77, Fortran 90, Fortran 95 or Fortran 2003. This file contains @dfn{source code}. @item Translate the user's program into instructions a computer can carry out more quickly than it takes to translate the instructions in the first place. The result after compilation of a program is @dfn{machine code}, code designed to be efficiently translated and processed by a machine such as your computer. Humans usually aren't as good writing machine code as they are at writing Fortran (or C++, Ada, or Java), because is easy to make tiny mistakes writing machine code. @item Provide the user with information about the reasons why the compiler is unable to create a binary from the source code. Usually this will be the case if the source code is flawed. When writing Fortran, it is easy to make big mistakes. The Fortran 90 requires that the compiler can point out mistakes to the user. An incorrect usage of the language causes an @dfn{error message}. The compiler will also attempt to diagnose cases where the user's program contains a correct usage of the language, but instructs the computer to do something questionable. This kind of diagnostics message is called a @dfn{warning message}. @item Provide optional information about the translation passes from the source code to machine code. This can help a user of the compiler to find the cause of certain bugs which may not be obvious in the source code, but may be more easily found at a lower level compiler output. It also helps developers to find bugs in the compiler itself. @item Provide information in the generated machine code that can make it easier to find bugs in the program (using a debugging tool, called a @dfn{debugger}, such as the GNU Debugger @command{gdb}). @item Locate and gather machine code already generated to perform actions requested by statements in the user's program. This machine code is organized into @dfn{modules} and is located and @dfn{linked} to the user program. @end itemize The GNU Fortran compiler consists of several components: @itemize @bullet @item A version of the @command{gcc} command (which also might be installed as the system's @command{cc} command) that also understands and accepts Fortran source code. The @command{gcc} command is the @dfn{driver} program for all the languages in the GNU Compiler Collection (GCC); With @command{gcc}, you can compile the source code of any language for which a front end is available in GCC. @item The @command{gfortran} command itself, which also might be installed as the system's @command{f95} command. @command{gfortran} is just another driver program, but specifically for the Fortran compiler only. The difference with @command{gcc} is that @command{gfortran} will automatically link the correct libraries to your program. @item A collection of run-time libraries. These libraries contain the machine code needed to support capabilities of the Fortran language that are not directly provided by the machine code generated by the @command{gfortran} compilation phase, such as intrinsic functions and subroutines, and routines for interaction with files and the operating system. @c and mechanisms to spawn, @c unleash and pause threads in parallelized code. @item The Fortran compiler itself, (@command{f951}). This is the GNU Fortran parser and code generator, linked to and interfaced with the GCC backend library. @command{f951} ``translates'' the source code to assembler code. You would typically not use this program directly; instead, the @command{gcc} or @command{gfortran} driver programs will call it for you. @end itemize @c --------------------------------------------------------------------- @c GNU Fortran and GCC @c --------------------------------------------------------------------- @node GNU Fortran and GCC @section GNU Fortran and GCC @cindex GNU Compiler Collection @cindex GCC GNU Fortran is a part of GCC, the @dfn{GNU Compiler Collection}. GCC consists of a collection of front ends for various languages, which translate the source code into a language-independent form called @dfn{GENERIC}. This is then processed by a common middle end which provides optimization, and then passed to one of a collection of back ends which generate code for different computer architectures and operating systems. Functionally, this is implemented with a driver program (@command{gcc}) which provides the command-line interface for the compiler. It calls the relevant compiler front-end program (e.g., @command{f951} for Fortran) for each file in the source code, and then calls the assembler and linker as appropriate to produce the compiled output. In a copy of GCC which has been compiled with Fortran language support enabled, @command{gcc} will recognize files with @file{.f}, @file{.f90}, @file{.f95}, and @file{.f03} extensions as Fortran source code, and compile it accordingly. A @command{gfortran} driver program is also provided, which is identical to @command{gcc} except that it automatically links the Fortran runtime libraries into the compiled program. This manual specifically documents the Fortran front end, which handles the programming language's syntax and semantics. The aspects of GCC which relate to the optimization passes and the back-end code generation are documented in the GCC manual; see @ref{Top,,Introduction,gcc,Using the GNU Compiler Collection (GCC)}. The two manuals together provide a complete reference for the GNU Fortran compiler. @c --------------------------------------------------------------------- @c GNU Fortran and G77 @c --------------------------------------------------------------------- @node GNU Fortran and G77 @section GNU Fortran and G77 @cindex Fortran 77 @cindex @command{g77} The GNU Fortran compiler is the successor to @command{g77}, the Fortran 77 front end included in GCC prior to version 4. It is an entirely new program that has been designed to provide Fortran 95 support and extensibility for future Fortran language standards, as well as providing backwards compatibility for Fortran 77 and nearly all of the GNU language extensions supported by @command{g77}. @c --------------------------------------------------------------------- @c Project Status @c --------------------------------------------------------------------- @node Project Status @section Project Status @quotation As soon as @command{gfortran} can parse all of the statements correctly, it will be in the ``larva'' state. When we generate code, the ``puppa'' state. When @command{gfortran} is done, we'll see if it will be a beautiful butterfly, or just a big bug.... --Andy Vaught, April 2000 @end quotation The start of the GNU Fortran 95 project was announced on the GCC homepage in March 18, 2000 (even though Andy had already been working on it for a while, of course). The GNU Fortran compiler is able to compile nearly all standard-compliant Fortran 95, Fortran 90, and Fortran 77 programs, including a number of standard and non-standard extensions, and can be used on real-world programs. In particular, the supported extensions include OpenMP, Cray-style pointers, and several Fortran 2003 features such as enumeration, stream I/O, and some of the enhancements to allocatable array support from TR 15581. However, it is still under development and has a few remaining rough edges. At present, the GNU Fortran compiler passes the @uref{http://www.fortran-2000.com/ArnaudRecipes/fcvs21_f95.html, NIST Fortran 77 Test Suite}, and produces acceptable results on the @uref{http://www.netlib.org/lapack/faq.html#1.21, LAPACK Test Suite}. It also provides respectable performance on the @uref{http://www.polyhedron.com/pb05.html, Polyhedron Fortran compiler benchmarks} and the @uref{http://www.llnl.gov/asci_benchmarks/asci/limited/lfk/README.html, Livermore Fortran Kernels test}. It has been used to compile a number of large real-world programs, including @uref{http://mysite.verizon.net/serveall/moene.pdf, the HIRLAM weather-forecasting code} and @uref{http://www.theochem.uwa.edu.au/tonto/, the Tonto quantum chemistry package}; see @url{http://gcc.gnu.org/wiki/GfortranApps} for an extended list. Among other things, the GNU Fortran compiler is intended as a replacement for G77. At this point, nearly all programs that could be compiled with G77 can be compiled with GNU Fortran, although there are a few minor known regressions. The primary work remaining to be done on GNU Fortran falls into three categories: bug fixing (primarily regarding the treatment of invalid code and providing useful error messages), improving the compiler optimizations and the performance of compiled code, and extending the compiler to support future standards---in particular, Fortran 2003. @c --------------------------------------------------------------------- @c Standards @c --------------------------------------------------------------------- @node Standards @section Standards @cindex Standards The GNU Fortran compiler implements ISO/IEC 1539:1997 (Fortran 95). As such, it can also compile essentially all standard-compliant Fortran 90 and Fortran 77 programs. It also supports the ISO/IEC TR-15581 enhancements to allocatable arrays, and the @uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf, OpenMP Application Program Interface v2.5} specification. In the future, the GNU Fortran compiler may also support other standard variants of and extensions to the Fortran language. These include ISO/IEC 1539-1:2004 (Fortran 2003). @c ===================================================================== @c PART I: INVOCATION REFERENCE @c ===================================================================== @tex \part{I}{Invoking GNU Fortran} @end tex @c --------------------------------------------------------------------- @c Compiler Options @c --------------------------------------------------------------------- @include invoke.texi @c --------------------------------------------------------------------- @c Runtime @c --------------------------------------------------------------------- @node Runtime @chapter Runtime: Influencing runtime behavior with environment variables @cindex environment variable The behavior of the @command{gfortran} can be influenced by environment variables. Malformed environment variables are silently ignored. @menu * GFORTRAN_STDIN_UNIT:: Unit number for standard input * GFORTRAN_STDOUT_UNIT:: Unit number for standard output * GFORTRAN_STDERR_UNIT:: Unit number for standard error * GFORTRAN_USE_STDERR:: Send library output to standard error * GFORTRAN_TMPDIR:: Directory for scratch files * GFORTRAN_UNBUFFERED_ALL:: Don't buffer output * GFORTRAN_SHOW_LOCUS:: Show location for runtime errors * GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted * GFORTRAN_DEFAULT_RECL:: Default record length for new files * GFORTRAN_LIST_SEPARATOR:: Separator for list output * GFORTRAN_CONVERT_UNIT:: Set endianness for unformatted I/O @end menu @node GFORTRAN_STDIN_UNIT @section @env{GFORTRAN_STDIN_UNIT}---Unit number for standard input This environment variable can be used to select the unit number preconnected to standard input. This must be a positive integer. The default value is 5. @node GFORTRAN_STDOUT_UNIT @section @env{GFORTRAN_STDOUT_UNIT}---Unit number for standard output This environment variable can be used to select the unit number preconnected to standard output. This must be a positive integer. The default value is 6. @node GFORTRAN_STDERR_UNIT @section @env{GFORTRAN_STDERR_UNIT}---Unit number for standard error This environment variable can be used to select the unit number preconnected to standard error. This must be a positive integer. The default value is 0. @node GFORTRAN_USE_STDERR @section @env{GFORTRAN_USE_STDERR}---Send library output to standard error This environment variable controls where library output is sent. If the first letter is @samp{y}, @samp{Y} or @samp{1}, standard error is used. If the first letter is @samp{n}, @samp{N} or @samp{0}, standard output is used. @node GFORTRAN_TMPDIR @section @env{GFORTRAN_TMPDIR}---Directory for scratch files This environment variable controls where scratch files are created. If this environment variable is missing, GNU Fortran searches for the environment variable @env{TMP}. If this is also missing, the default is @file{/tmp}. @node GFORTRAN_UNBUFFERED_ALL @section @env{GFORTRAN_UNBUFFERED_ALL}---Don't buffer output This environment variable controls whether all output is unbuffered. If the first letter is @samp{y}, @samp{Y} or @samp{1}, all output is unbuffered. This will slow down large writes. If the first letter is @samp{n}, @samp{N} or @samp{0}, output is buffered. This is the default. @node GFORTRAN_SHOW_LOCUS @section @env{GFORTRAN_SHOW_LOCUS}---Show location for runtime errors If the first letter is @samp{y}, @samp{Y} or @samp{1}, filename and line numbers for runtime errors are printed. If the first letter is @samp{n}, @samp{N} or @samp{0}, don't print filename and line numbers for runtime errors. The default is to print the location. @node GFORTRAN_OPTIONAL_PLUS @section @env{GFORTRAN_OPTIONAL_PLUS}---Print leading + where permitted If the first letter is @samp{y}, @samp{Y} or @samp{1}, a plus sign is printed where permitted by the Fortran standard. If the first letter is @samp{n}, @samp{N} or @samp{0}, a plus sign is not printed in most cases. Default is not to print plus signs. @node GFORTRAN_DEFAULT_RECL @section @env{GFORTRAN_DEFAULT_RECL}---Default record length for new files This environment variable specifies the default record length, in bytes, for files which are opened without a @code{RECL} tag in the @code{OPEN} statement. This must be a positive integer. The default value is 1073741824 bytes (1 GB). @node GFORTRAN_LIST_SEPARATOR @section @env{GFORTRAN_LIST_SEPARATOR}---Separator for list output This environment variable specifies the separator when writing list-directed output. It may contain any number of spaces and at most one comma. If you specify this on the command line, be sure to quote spaces, as in @smallexample $ GFORTRAN_LIST_SEPARATOR=' , ' ./a.out @end smallexample when @command{a.out} is the compiled Fortran program that you want to run. Default is a single space. @node GFORTRAN_CONVERT_UNIT @section @env{GFORTRAN_CONVERT_UNIT}---Set endianness for unformatted I/O By setting the @env{GFORTRAN_CONVERT_UNIT} variable, it is possible to change the representation of data for unformatted files. The syntax for the @env{GFORTRAN_CONVERT_UNIT} variable is: @smallexample GFORTRAN_CONVERT_UNIT: mode | mode ';' exception ; mode: 'native' | 'swap' | 'big_endian' | 'little_endian' ; exception: mode ':' unit_list | unit_list ; unit_list: unit_spec | unit_list unit_spec ; unit_spec: INTEGER | INTEGER '-' INTEGER ; @end smallexample The variable consists of an optional default mode, followed by a list of optional exceptions, which are separated by semicolons from the preceding default and each other. Each exception consists of a format and a comma-separated list of units. Valid values for the modes are the same as for the @code{CONVERT} specifier: @itemize @w{} @item @code{NATIVE} Use the native format. This is the default. @item @code{SWAP} Swap between little- and big-endian. @item @code{LITTLE_ENDIAN} Use the little-endian format for unformatted files. @item @code{BIG_ENDIAN} Use the big-endian format for unformatted files. @end itemize A missing mode for an exception is taken to mean @code{BIG_ENDIAN}. Examples of values for @env{GFORTRAN_CONVERT_UNIT} are: @itemize @w{} @item @code{'big_endian'} Do all unformatted I/O in big_endian mode. @item @code{'little_endian;native:10-20,25'} Do all unformatted I/O in little_endian mode, except for units 10 to 20 and 25, which are in native format. @item @code{'10-20'} Units 10 to 20 are big-endian, the rest is native. @end itemize Setting the environment variables should be done on the command line or via the @command{export} command for @command{sh}-compatible shells and via @command{setenv} for @command{csh}-compatible shells. Example for @command{sh}: @smallexample $ gfortran foo.f90 $ GFORTRAN_CONVERT_UNIT='big_endian;native:10-20' ./a.out @end smallexample Example code for @command{csh}: @smallexample % gfortran foo.f90 % setenv GFORTRAN_CONVERT_UNIT 'big_endian;native:10-20' % ./a.out @end smallexample Using anything but the native representation for unformatted data carries a significant speed overhead. If speed in this area matters to you, it is best if you use this only for data that needs to be portable. @xref{CONVERT specifier}, for an alternative way to specify the data representation for unformatted files. @xref{Runtime Options}, for setting a default data representation for the whole program. The @code{CONVERT} specifier overrides the @option{-fconvert} compile options. @c ===================================================================== @c PART II: LANGUAGE REFERENCE @c ===================================================================== @tex \part{II}{Language Reference} @end tex @c --------------------------------------------------------------------- @c Fortran 2003 Status @c --------------------------------------------------------------------- @node Fortran 2003 status @chapter Fortran 2003 Status Although GNU Fortran focuses on implementing the Fortran 95 standard for the time being, a few Fortran 2003 features are currently available. @itemize @item Intrinsics @code{command_argument_count}, @code{get_command}, @code{get_command_argument}, @code{get_environment_variable}, and @code{move_alloc}. @item @cindex array, constructors @cindex @code{[...]} Array constructors using square brackets. That is, @code{[...]} rather than @code{(/.../)}. @item @cindex @code{FLUSH} statement @cindex statement, @code{FLUSH} @code{FLUSH} statement. @item @cindex @code{IOMSG=} specifier @code{IOMSG=} specifier for I/O statements. @item @cindex @code{ENUM} statement @cindex @code{ENUMERATOR} statement @cindex statement, @code{ENUM} @cindex statement, @code{ENUMERATOR} @opindex @code{fshort-enums} Support for the declaration of enumeration constants via the @code{ENUM} and @code{ENUMERATOR} statements. Interoperability with @command{gcc} is guaranteed also for the case where the @command{-fshort-enums} command line option is given. @item @cindex TR 15581 TR 15581: @itemize @item @cindex @code{ALLOCATABLE} dummy arguments @code{ALLOCATABLE} dummy arguments. @item @cindex @code{ALLOCATABLE} function results @code{ALLOCATABLE} function results @item @cindex @code{ALLOCATABLE} components of derived types @code{ALLOCATABLE} components of derived types @end itemize @item @cindex @code{STREAM} I/O @cindex @code{ACCESS='STREAM'} I/O The @code{OPEN} statement supports the @code{ACCESS='STREAM'} specifier, allowing I/O without any record structure. @item Namelist input/output for internal files. @item @cindex @code{PROTECTED} statement @cindex statement, @code{PROTECTED} The @code{PROTECTED} statement and attribute. @item @cindex @code{VALUE} statement @cindex statement, @code{VALUE} The @code{VALUE} statement and attribute. @item @cindex @code{VOLATILE} statement @cindex statement, @code{VOLATILE} The @code{VOLATILE} statement and attribute. @item @cindex @code{IMPORT} statement @cindex statement, @code{IMPORT} The @code{IMPORT} statement, allowing to import host-associated derived types. @item @cindex @code{USE, INTRINSIC} statement @cindex statement, @code{USE, INTRINSIC} @cindex @code{ISO_FORTRAN_ENV} statement @cindex statement, @code{ISO_FORTRAN_ENV} @code{USE} statement with @code{INTRINSIC} and @code{NON_INTRINSIC} attribute; supported intrinsic modules: @code{ISO_FORTRAN_ENV}, @code{OMP_LIB} and @code{OMP_LIB_KINDS}. @item Renaming of operators in the @code{USE} statement. @end itemize @c --------------------------------------------------------------------- @c Extensions @c --------------------------------------------------------------------- @c Maybe this chapter should be merged with the 'Standards' section, @c whenever that is written :-) @node Extensions @chapter Extensions @cindex Extension GNU Fortran implements a number of extensions over standard Fortran. This chapter contains information on their syntax and meaning. There are currently two categories of GNU Fortran extensions, those that provide functionality beyond that provided by any standard, and those that are supported by GNU Fortran purely for backward compatibility with legacy compilers. By default, @option{-std=gnu} allows the compiler to accept both types of extensions, but to warn about the use of the latter. Specifying either @option{-std=f95} or @option{-std=f2003} disables both types of extensions, and @option{-std=legacy} allows both without warning. @menu * Old-style kind specifications:: * Old-style variable initialization:: * Extensions to namelist:: * X format descriptor without count field:: * Commas in FORMAT specifications:: * Missing period in FORMAT specifications:: * I/O item lists:: * BOZ literal constants:: * Real array indices:: * Unary operators:: * Implicitly convert LOGICAL and INTEGER values:: * Hollerith constants support:: * Cray pointers:: * CONVERT specifier:: * OpenMP:: * Argument list functions:: @end menu @node Old-style kind specifications @section Old-style kind specifications @cindex kind, old-style GNU Fortran allows old-style kind specifications in declarations. These look like: @smallexample TYPESPEC*size x,y,z @end smallexample @noindent where @code{TYPESPEC} is a basic type (@code{INTEGER}, @code{REAL}, etc.), and where @code{size} is a byte count corresponding to the storage size of a valid kind for that type. (For @code{COMPLEX} variables, @code{size} is the total size of the real and imaginary parts.) The statement then declares @code{x}, @code{y} and @code{z} to be of type @code{TYPESPEC} with the appropriate kind. This is equivalent to the standard-conforming declaration @smallexample TYPESPEC(k) x,y,z @end smallexample @noindent where @code{k} is equal to @code{size} for most types, but is equal to @code{size/2} for the @code{COMPLEX} type. @node Old-style variable initialization @section Old-style variable initialization GNU Fortran allows old-style initialization of variables of the form: @smallexample INTEGER i/1/,j/2/ REAL x(2,2) /3*0.,1./ @end smallexample The syntax for the initializers is as for the @code{DATA} statement, but unlike in a @code{DATA} statement, an initializer only applies to the variable immediately preceding the initialization. In other words, something like @code{INTEGER I,J/2,3/} is not valid. This style of initialization is only allowed in declarations without double colons (@code{::}); the double colons were introduced in Fortran 90, which also introduced a standard syntax for initializing variables in type declarations. Examples of standard-conforming code equivalent to the above example are: @smallexample ! Fortran 90 INTEGER :: i = 1, j = 2 REAL :: x(2,2) = RESHAPE((/0.,0.,0.,1./),SHAPE(x)) ! Fortran 77 INTEGER i, j REAL x(2,2) DATA i/1/, j/2/, x/3*0.,1./ @end smallexample Note that variables which are explicitly initialized in declarations or in @code{DATA} statements automatically acquire the @code{SAVE} attribute. @node Extensions to namelist @section Extensions to namelist @cindex Namelist GNU Fortran fully supports the Fortran 95 standard for namelist I/O including array qualifiers, substrings and fully qualified derived types. The output from a namelist write is compatible with namelist read. The output has all names in upper case and indentation to column 1 after the namelist name. Two extensions are permitted: Old-style use of @samp{$} instead of @samp{&} @smallexample $MYNML X(:)%Y(2) = 1.0 2.0 3.0 CH(1:4) = "abcd" $END @end smallexample It should be noted that the default terminator is @samp{/} rather than @samp{&END}. Querying of the namelist when inputting from stdin. After at least one space, entering @samp{?} sends to stdout the namelist name and the names of the variables in the namelist: @smallexample ? &mynml x x%y ch &end @end smallexample Entering @samp{=?} outputs the namelist to stdout, as if @code{WRITE(*,NML = mynml)} had been called: @smallexample =? &MYNML X(1)%Y= 0.000000 , 1.000000 , 0.000000 , X(2)%Y= 0.000000 , 2.000000 , 0.000000 , X(3)%Y= 0.000000 , 3.000000 , 0.000000 , CH=abcd, / @end smallexample To aid this dialog, when input is from stdin, errors send their messages to stderr and execution continues, even if @code{IOSTAT} is set. @code{PRINT} namelist is permitted. This causes an error if @option{-std=f95} is used. @smallexample PROGRAM test_print REAL, dimension (4) :: x = (/1.0, 2.0, 3.0, 4.0/) NAMELIST /mynml/ x PRINT mynml END PROGRAM test_print @end smallexample Expanded namelist reads are permitted. This causes an error if @option{-std=f95} is used. In the following example, the first element of the array will be given the value 0.00 and the two succeeding elements will be given the values 1.00 and 2.00. @smallexample &MYNML X(1,1) = 0.00 , 1.00 , 2.00 / @end smallexample @node X format descriptor without count field @section @code{X} format descriptor without count field To support legacy codes, GNU Fortran permits the count field of the @code{X} edit descriptor in @code{FORMAT} statements to be omitted. When omitted, the count is implicitly assumed to be one. @smallexample PRINT 10, 2, 3 10 FORMAT (I1, X, I1) @end smallexample @node Commas in FORMAT specifications @section Commas in @code{FORMAT} specifications To support legacy codes, GNU Fortran allows the comma separator to be omitted immediately before and after character string edit descriptors in @code{FORMAT} statements. @smallexample PRINT 10, 2, 3 10 FORMAT ('FOO='I1' BAR='I2) @end smallexample @node Missing period in FORMAT specifications @section Missing period in @code{FORMAT} specifications To support legacy codes, GNU Fortran allows missing periods in format specifications if and only if @option{-std=legacy} is given on the command line. This is considered non-conforming code and is discouraged. @smallexample REAL :: value READ(*,10) value 10 FORMAT ('F4') @end smallexample @node I/O item lists @section I/O item lists @cindex I/O item lists To support legacy codes, GNU Fortran allows the input item list of the @code{READ} statement, and the output item lists of the @code{WRITE} and @code{PRINT} statements, to start with a comma. @node BOZ literal constants @section BOZ literal constants @cindex BOZ literal constants As an extension, GNU Fortran allows hexadecimal BOZ literal constants to be specified using the X prefix, in addition to the standard Z prefix. BOZ literal constants can also be specified by adding a suffix to the string. For example, @code{Z'ABC'} and @code{'ABC'Z} are equivalent. The Fortran standard restricts the appearance of a BOZ literal constant to the @code{DATA} statement, and it is expected to be assigned to an @code{INTEGER} variable. GNU Fortran permits a BOZ literal to appear in any initialization expression as well as assignment statements. Attempts to use a BOZ literal constant to do a bitwise initialization of a variable can lead to confusion. A BOZ literal constant is converted to an @code{INTEGER} value with the kind type with the largest decimal representation, and this value is then converted numerically to the type and kind of the variable in question. Thus, one should not expect a bitwise copy of the BOZ literal constant to be assigned to a @code{REAL} variable. Similarly, initializing an @code{INTEGER} variable with a statement such as @code{DATA i/Z'FFFFFFFF'/} will produce an integer overflow rather than the desired result of @math{-1} when @code{i} is a 32-bit integer on a system that supports 64-bit integers. The @samp{-fno-range-check} option can be used as a workaround for legacy code that initializes integers in this manner. @node Real array indices @section Real array indices @cindex array, indices of type real As an extension, GNU Fortran allows the use of @code{REAL} expressions or variables as array indices. @node Unary operators @section Unary operators @cindex operators, unary As an extension, GNU Fortran allows unary plus and unary minus operators to appear as the second operand of binary arithmetic operators without the need for parenthesis. @smallexample X = Y * -Z @end smallexample @node Implicitly convert LOGICAL and INTEGER values @section Implicitly convert @code{LOGICAL} and @code{INTEGER} values @cindex conversion, to integer @cindex conversion, to logical As an extension for backwards compatibility with other compilers, GNU Fortran allows the implicit conversion of @code{LOGICAL} values to @code{INTEGER} values and vice versa. When converting from a @code{LOGICAL} to an @code{INTEGER}, @code{.FALSE.} is interpreted as zero, and @code{.TRUE.} is interpreted as one. When converting from @code{INTEGER} to @code{LOGICAL}, the value zero is interpreted as @code{.FALSE.} and any nonzero value is interpreted as @code{.TRUE.}. @smallexample INTEGER :: i = 1 IF (i) PRINT *, 'True' @end smallexample @node Hollerith constants support @section Hollerith constants support @cindex Hollerith constants GNU Fortran supports Hollerith constants in assignments, function arguments, and @code{DATA} and @code{ASSIGN} statements. A Hollerith constant is written as a string of characters preceded by an integer constant indicating the character count, and the letter @code{H} or @code{h}, and stored in bytewise fashion in a numeric (@code{INTEGER}, @code{REAL}, or @code{complex}) or @code{LOGICAL} variable. The constant will be padded or truncated to fit the size of the variable in which it is stored. Examples of valid uses of Hollerith constants: @smallexample complex*16 x(2) data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/ x(1) = 16HABCDEFGHIJKLMNOP call foo (4h abc) @end smallexample Invalid Hollerith constants examples: @smallexample integer*4 a a = 8H12345678 ! Valid, but the Hollerith constant will be truncated. a = 0H ! At least one character is needed. @end smallexample In general, Hollerith constants were used to provide a rudimentary facility for handling character strings in early Fortran compilers, prior to the introduction of @code{CHARACTER} variables in Fortran 77; in those cases, the standard-compliant equivalent is to convert the program to use proper character strings. On occasion, there may be a case where the intent is specifically to initialize a numeric variable with a given byte sequence. In these cases, the same result can be obtained by using the @code{TRANSFER} statement, as in this example. @smallexample INTEGER(KIND=4) :: a a = TRANSFER ("abcd", a) ! equivalent to: a = 4Habcd @end smallexample @node Cray pointers @section Cray pointers @cindex pointer, cray Cray pointers are part of a non-standard extension that provides a C-like pointer in Fortran. This is accomplished through a pair of variables: an integer "pointer" that holds a memory address, and a "pointee" that is used to dereference the pointer. Pointer/pointee pairs are declared in statements of the form: @smallexample pointer ( , ) @end smallexample or, @smallexample pointer ( , ), ( , ), ... @end smallexample The pointer is an integer that is intended to hold a memory address. The pointee may be an array or scalar. A pointee can be an assumed size array---that is, the last dimension may be left unspecified by using a @code{*} in place of a value---but a pointee cannot be an assumed shape array. No space is allocated for the pointee. The pointee may have its type declared before or after the pointer statement, and its array specification (if any) may be declared before, during, or after the pointer statement. The pointer may be declared as an integer prior to the pointer statement. However, some machines have default integer sizes that are different than the size of a pointer, and so the following code is not portable: @smallexample integer ipt pointer (ipt, iarr) @end smallexample If a pointer is declared with a kind that is too small, the compiler will issue a warning; the resulting binary will probably not work correctly, because the memory addresses stored in the pointers may be truncated. It is safer to omit the first line of the above example; if explicit declaration of ipt's type is omitted, then the compiler will ensure that ipt is an integer variable large enough to hold a pointer. Pointer arithmetic is valid with Cray pointers, but it is not the same as C pointer arithmetic. Cray pointers are just ordinary integers, so the user is responsible for determining how many bytes to add to a pointer in order to increment it. Consider the following example: @smallexample real target(10) real pointee(10) pointer (ipt, pointee) ipt = loc (target) ipt = ipt + 1 @end smallexample The last statement does not set @code{ipt} to the address of @code{target(1)}, as it would in C pointer arithmetic. Adding @code{1} to @code{ipt} just adds one byte to the address stored in @code{ipt}. Any expression involving the pointee will be translated to use the value stored in the pointer as the base address. To get the address of elements, this extension provides an intrinsic function @code{LOC()}. The @code{LOC()} function is equivalent to the @code{&} operator in C, except the address is cast to an integer type: @smallexample real ar(10) pointer(ipt, arpte(10)) real arpte ipt = loc(ar) ! Makes arpte is an alias for ar arpte(1) = 1.0 ! Sets ar(1) to 1.0 @end smallexample The pointer can also be set by a call to the @code{MALLOC} intrinsic (see @ref{MALLOC}). Cray pointees often are used to alias an existing variable. For example: @smallexample integer target(10) integer iarr(10) pointer (ipt, iarr) ipt = loc(target) @end smallexample As long as @code{ipt} remains unchanged, @code{iarr} is now an alias for @code{target}. The optimizer, however, will not detect this aliasing, so it is unsafe to use @code{iarr} and @code{target} simultaneously. Using a pointee in any way that violates the Fortran aliasing rules or assumptions is illegal. It is the user's responsibility to avoid doing this; the compiler works under the assumption that no such aliasing occurs. Cray pointers will work correctly when there is no aliasing (i.e., when they are used to access a dynamically allocated block of memory), and also in any routine where a pointee is used, but any variable with which it shares storage is not used. Code that violates these rules may not run as the user intends. This is not a bug in the optimizer; any code that violates the aliasing rules is illegal. (Note that this is not unique to GNU Fortran; any Fortran compiler that supports Cray pointers will ``incorrectly'' optimize code with illegal aliasing.) There are a number of restrictions on the attributes that can be applied to Cray pointers and pointees. Pointees may not have the @code{ALLOCATABLE}, @code{INTENT}, @code{OPTIONAL}, @code{DUMMY}, @code{TARGET}, @code{INTRINSIC}, or @code{POINTER} attributes. Pointers may not have the @code{DIMENSION}, @code{POINTER}, @code{TARGET}, @code{ALLOCATABLE}, @code{EXTERNAL}, or @code{INTRINSIC} attributes. Pointees may not occur in more than one pointer statement. A pointee cannot be a pointer. Pointees cannot occur in equivalence, common, or data statements. A Cray pointer may also point to a function or a subroutine. For example, the following excerpt is valid: @smallexample implicit none external sub pointer (subptr,subpte) external subpte subptr = loc(sub) call subpte() [...] subroutine sub [...] end subroutine sub @end smallexample A pointer may be modified during the course of a program, and this will change the location to which the pointee refers. However, when pointees are passed as arguments, they are treated as ordinary variables in the invoked function. Subsequent changes to the pointer will not change the base address of the array that was passed. @node CONVERT specifier @section CONVERT specifier @cindex CONVERT specifier GNU Fortran allows the conversion of unformatted data between little- and big-endian representation to facilitate moving of data between different systems. The conversion can be indicated with the @code{CONVERT} specifier on the @code{OPEN} statement. @xref{GFORTRAN_CONVERT_UNIT}, for an alternative way of specifying the data format via an environment variable. Valid values for @code{CONVERT} are: @itemize @w{} @item @code{CONVERT='NATIVE'} Use the native format. This is the default. @item @code{CONVERT='SWAP'} Swap between little- and big-endian. @item @code{CONVERT='LITTLE_ENDIAN'} Use the little-endian representation for unformatted files. @item @code{CONVERT='BIG_ENDIAN'} Use the big-endian representation for unformatted files. @end itemize Using the option could look like this: @smallexample open(file='big.dat',form='unformatted',access='sequential', & convert='big_endian') @end smallexample The value of the conversion can be queried by using @code{INQUIRE(CONVERT=ch)}. The values returned are @code{'BIG_ENDIAN'} and @code{'LITTLE_ENDIAN'}. @code{CONVERT} works between big- and little-endian for @code{INTEGER} values of all supported kinds and for @code{REAL} on IEEE systems of kinds 4 and 8. Conversion between different ``extended double'' types on different architectures such as m68k and x86_64, which GNU Fortran supports as @code{REAL(KIND=10)} and @code{REAL(KIND=16)}, will probably not work. @emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT environment variable will override the CONVERT specifier in the open statement}. This is to give control over data formats to users who do not have the source code of their program available. Using anything but the native representation for unformatted data carries a significant speed overhead. If speed in this area matters to you, it is best if you use this only for data that needs to be portable. @node OpenMP @section OpenMP @cindex OpenMP GNU Fortran attempts to be OpenMP Application Program Interface v2.5 compatible when invoked with the @option{-fopenmp} option. GNU Fortran then generates parallelized code according to the OpenMP directives used in the source. The OpenMP Fortran runtime library routines are provided both in a form of a Fortran 90 module named @code{omp_lib} and in a form of a Fortran @code{include} file named @file{omp_lib.h}. For details refer to the actual @uref{http://www.openmp.org/drupal/mp-documents/spec25.pdf, OpenMP Application Program Interface v2.5} specification. @node Argument list functions @section Argument list functions %VAL, %REF and %LOC @cindex argument list functions @cindex %VAL @cindex %REF @cindex %LOC GNU Fortran supports argument list functions @code{%VAL}, @code{%REF} and @code{%LOC} statements, for backward compatibility with g77. It is recommended that these should be used only for code that is accessing facilities outside of GNU Fortran, such as operating system or windowing facilities. It is best to constrain such uses to isolated portions of a program--portions that deal specifically and exclusively with low-level, system-dependent facilities. Such portions might well provide a portable interface for use by the program as a whole, but are themselves not portable, and should be thoroughly tested each time they are rebuilt using a new compiler or version of a compiler. @code{%VAL} passes a scalar argument by value, @code{%REF} passes it by reference and @code{%LOC} passes its memory location. Since gfortran already passes scalar arguments by reference, @code{%REF} is in effect a do-nothing. @code{%LOC} has the same effect as a fortran pointer. An example of passing an argument by value to a C subroutine foo.: @smallexample C C prototype void foo_ (float x); C external foo real*4 x x = 3.14159 call foo (%VAL (x)) end @end smallexample For details refer to the g77 manual @uref{http://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/index.html#Top}. Also, the gfortran testsuite c_by_val.f and its partner c_by_val.c are worth a look. @c --------------------------------------------------------------------- @c Intrinsic Procedures @c --------------------------------------------------------------------- @include intrinsic.texi @tex \blankpart @end tex @c --------------------------------------------------------------------- @c Contributing @c --------------------------------------------------------------------- @node Contributing @unnumbered Contributing @cindex Contributing Free software is only possible if people contribute to efforts to create it. We're always in need of more people helping out with ideas and comments, writing documentation and contributing code. If you want to contribute to GNU Fortran, have a look at the long lists of projects you can take on. Some of these projects are small, some of them are large; some are completely orthogonal to the rest of what is happening on GNU Fortran, but others are ``mainstream'' projects in need of enthusiastic hackers. All of these projects are important! We'll eventually get around to the things here, but they are also things doable by someone who is willing and able. @menu * Contributors:: * Projects:: * Proposed Extensions:: @end menu @node Contributors @section Contributors to GNU Fortran @cindex Contributors @cindex Credits @cindex Authors Most of the parser was hand-crafted by @emph{Andy Vaught}, who is also the initiator of the whole project. Thanks Andy! Most of the interface with GCC was written by @emph{Paul Brook}. The following individuals have contributed code and/or ideas and significant help to the GNU Fortran project (in no particular order): @itemize @minus @item Andy Vaught @item Katherine Holcomb @item Tobias Schl@"uter @item Steven Bosscher @item Toon Moene @item Tim Prince @item Niels Kristian Bech Jensen @item Steven Johnson @item Paul Brook @item Feng Wang @item Bud Davis @item Paul Thomas @item Fran@,{c}ois-Xavier Coudert @item Steven G. Kargl @item Jerry Delisle @item Janne Blomqvist @item Erik Edelmann @item Thomas Koenig @item Asher Langton @item Jakub Jelinek @item Roger Sayle @item H.J. Lu @item Richard Henderson @item Richard Sandiford @item Richard Guenther @item Bernhard Fischer @end itemize The following people have contributed bug reports, smaller or larger patches, and much needed feedback and encouragement for the GNU Fortran project: @itemize @minus @item Erik Schnetter @item Bill Clodius @item Kate Hedstrom @end itemize Many other individuals have helped debug, test and improve the GNU Fortran compiler over the past few years, and we welcome you to do the same! If you already have done so, and you would like to see your name listed in the list above, please contact us. @node Projects @section Projects @table @emph @item Help build the test suite Solicit more code for donation to the test suite. We can keep code private on request. @item Bug hunting/squishing Find bugs and write more test cases! Test cases are especially very welcome, because it allows us to concentrate on fixing bugs instead of isolating them. @item Smaller projects (``bug'' fixes): @itemize @minus @item Allow init exprs to be numbers raised to integer powers. @item Implement correct rounding. @item Implement F restrictions on Fortran 95 syntax. @item See about making Emacs-parsable error messages. @end itemize @end table If you wish to work on the runtime libraries, please contact a project maintainer. @c TODO: email! @node Proposed Extensions @section Proposed Extensions Here's a list of proposed extensions for the GNU Fortran compiler, in no particular order. Most of these are necessary to be fully compatible with existing Fortran compilers, but they are not part of the official J3 Fortran 95 standard. @subsection Compiler extensions: @itemize @bullet @item User-specified alignment rules for structures. @item Flag to generate @code{Makefile} info. @item Automatically extend single precision constants to double. @item Compile code that conserves memory by dynamically allocating common and module storage either on stack or heap. @item Compile flag to generate code for array conformance checking (suggest -CC). @item User control of symbol names (underscores, etc). @item Compile setting for maximum size of stack frame size before spilling parts to static or heap. @item Flag to force local variables into static space. @item Flag to force local variables onto stack. @item Flag for maximum errors before ending compile. @item Option to initialize otherwise uninitialized integer and floating point variables. @end itemize @subsection Environment Options @itemize @bullet @item Pluggable library modules for random numbers, linear algebra. LA should use BLAS calling conventions. @item Environment variables controlling actions on arithmetic exceptions like overflow, underflow, precision loss---Generate NaN, abort, default. action. @item Set precision for fp units that support it (i387). @item Variable for setting fp rounding mode. @item Variable to fill uninitialized variables with a user-defined bit pattern. @item Environment variable controlling filename that is opened for that unit number. @item Environment variable to clear/trash memory being freed. @item Environment variable to control tracing of allocations and frees. @item Environment variable to display allocated memory at normal program end. @item Environment variable for filename for * IO-unit. @item Environment variable for temporary file directory. @item Environment variable forcing standard output to be line buffered (unix). @end itemize @c --------------------------------------------------------------------- @c GNU General Public License @c --------------------------------------------------------------------- @include gpl.texi @c --------------------------------------------------------------------- @c GNU Free Documentation License @c --------------------------------------------------------------------- @include fdl.texi @c --------------------------------------------------------------------- @c Funding Free Software @c --------------------------------------------------------------------- @include funding.texi @c --------------------------------------------------------------------- @c Indices @c --------------------------------------------------------------------- @node Option Index @unnumbered Option Index @command{gfortran}'s command line options are indexed here without any initial @samp{-} or @samp{--}. Where an option has both positive and negative forms (such as -foption and -fno-option), relevant entries in the manual are indexed under the most appropriate form; it may sometimes be useful to look up both forms. @printindex op @node Keyword Index @unnumbered Keyword Index @printindex cp @bye